Meteorites that have fallen to Earth contain some of the most primitive stuff of life, a new study has found.

Contrary to popular belief, they are packed with ancient carbon-rich (organic) molecules that were essential for life to get started on Earth.

Until now, it was thought such matter, which was formed before our Solar System came into existence, could only be found in interstellar dust.

The Carnegie Institution of Washington study is reported in Science magazine.

It challenges the notion that the only way we can investigate our molecular origins is to try to collect samples of unaltered cosmic material from space - the driving force behind missions such as Stardust.

Instead, the Carnegie team argues that primitive organic materials - essentially unaltered components of the original building blocks of the Solar System - can be found in the pieces of interplanetary rock and metal that land on our planet.

Organic 'fingerprints'

The US scientists analysed six carbonaceous chondrite meteorites - the oldest type known.

It was thought meteorites would contain only altered material

Using new techniques, the researchers looked at the relative proportions of different types (isotopes) of nitrogen and hydrogen atoms associated with the meteorites' organic matter.

Their analysis found regions where there was an excess of the heavier forms of these elements - something also found in interstellar dust grains.

It suggested, therefore, that the meteorites contained material that had been largely unaltered since the time when the Solar System was formed from the collapse of a giant cloud of gas and dust called the solar nebula.

"It's amazing that pristine organic molecules associated with these isotopes were able to survive the harsh and tumultuous conditions present in the inner Solar System when the meteorites that contain them came together," said Carnegie researcher Conel Alexander.

"It means that the parent bodies - the comets and asteroids - of these seemingly different types of extraterrestrial material are more similar in origin than previously believed."

Elusive time period

The discovery opens up a new window to study a long-gone era.

We could be looking at the remnants of precursor organic molecules, formed in the interstellar medium before the Solar System even existed

Prof Ian Wright

"Before, we could only explore minute samples from interplanetary dust particles (IDPs)," said the lead author of the Science paper, Henner Busemann.

"Our discovery now allows us to extract large amounts of this material from meteorites, which are large and contain several percent of carbon, instead of from IDPs, which are on the order of a million, million times less massive."

The scientists believe that further investigation of meteorites may yield enough material to perform experiments that would not be possible with the tiny primitive organic grains from interplanetary dust particles or cometary grains returned by the US space agency's (Nasa) Stardust mission.

Pre-solar origin

UK planetary expert Ian Wright, of the Open University in Milton Keynes, believes we now have the potential to be able to study pre-solar organic molecules in the laboratory.

"That organic molecules in carbonaceous chondrites are, at least in part, pre-solar in origin, is not a new idea," he told the BBC News website.

"What is presented here are data that show that the distribution of isotopic compositions within the organic complex is [highly varied].

"I guess it is possible that we could be looking at the remnants of precursor organic molecules, formed in the interstellar medium before the Solar System even existed, embedded in a complex that formed at a later time (perhaps within the solar nebula itself)."